Recent years have witnessed practical use of a flat-panel display in various products and fields. This has led to a demand for a flat-panel display that is larger in size, achieves higher image quality, and consumes less power.
Under such circumstances, great attention has been drawn to an organic EL display device that (i) includes an organic electroluminescence (hereinafter abbreviated to “EL”) element which uses EL of an organic material and that (ii) is an all-solid-state flat-panel display which is excellent in, for example, low-voltage driving, high-speed response, self-emitting, and wide viewing angle characteristics.
An organic EL display device includes, for example, (i) a substrate made up of members such as a glass substrate and TFTs (thin film transistors) provided to the glass substrate and (ii) organic EL elements provided on the substrate and connected to the TFTs.
For example, a full-color organic EL display device typically includes, as sub-pixels aligned on a substrate, organic EL elements including luminescent layers of red (R), green (G), and blue (B). The full-color organic EL display device carries out an image display by, with use of TFTs, selectively causing the organic EL elements to each emit light with a desired luminance.
In order to produce an organic EL display device, it is therefore necessary to form, for each organic EL element, a luminescent layer of a predetermined pattern made of an organic luminescent material which emits light of the colors.
Such formation of a luminescent layer of a predetermined pattern is performed by a method such as (i) a vacuum vapor deposition method, (ii) an inkjet method, and (iii) a laser transfer method. The production of, for example, a low-molecular organic EL display (OLED) often uses a vapor deposition method.
The vacuum vapor deposition method uses a mask (referred to also as a shadow mask) provided with openings of a predetermined pattern. The mask is fixed in close contact with a vapor-deposited surface of a substrate which vapor-deposited surface faces a vapor deposition source.
Then, vapor deposition particles (film formation material) are injected from the vapor deposition source so as to be deposited on the vapor-deposited surface through openings of the mask. This forms a thin film of a predetermined pattern. The vapor deposition is carried out for each color of a luminescent layer. This is called “selective vapor deposition”.
Patent Literatures 1 and 2 each disclose a selective vapor deposition method in which luminescent layers of respective colors are formed by shifting a mask bit by bit with respect to a substrate.
Such a conventional selective vapor deposition method uses a mask that has a substantially same size as a substrate. During vapor deposition, the mask is fixed so as to cover a vapor-deposited surface of the substrate.
Accordingly, the conventional selective vapor deposition method necessitates increasing a mask size as a substrate size increases.
However, an increase in mask size causes self-weight bending and extension of the mask. This is more likely to generate a gap, whose size varies depending on a position on the vapor-deposited surface of the substrate, between the substrate and the mask.
Use of the conventional selective vapor deposition method therefore makes it difficult to perform precise patterning, thereby causing problems such as misplacement of vapor deposition and color mixture.
Moreover, according to the conventional selective vapor deposition method, the increase in mask size leads to an increase in size and weight of members such as a frame holding the mask and the like. This makes handling of these members difficult, thereby threatening productivity and safety.
According to the conventional selective vapor deposition method, a vapor deposition device and accompanying devices also increase in size and become complicated. This makes device designing difficult and makes a device installation cost expensive.
As described above, according to the conventional selective vapor deposition method, it is difficult to form a deposition film patterned with high definition on a large-size substrate. For example, selective vapor deposition at a mass production level has not been established yet for a large-size substrate for which a 60-inch or larger mask is used.